I work with Linux Mint 19.1 installed on thin clients. But I had a problem with the kernel 4.15 (VoIP connected on an Ethernet port doesn't work correctly) so I changed the kernel to 4.4 to solve that. When I changed the kernel, the HDMI audio fails. I tried many things to fix this, but I could not.

I installed pavucontrol on the PC, then noticed something weird.
With the 4.15 kernel, the status port is plugged in, but with kernel 4.4, the status port is unplugged. Details follow below: